Grid for electron-discharge tubes



E. SCHRACK GRID FOR ELECTRON DISCHARGE TUBES Dec'. 27, 1927.

Filed Feb. 13, 1925 Patented Dec. 27, 1927.

UNITED STATES 1,654,471 PATENT OFFICE.

nnunnn scnancx, or VIENNA, Austrian.

GRID FOR ELECTRON-DISCHARGE TUBES.

Application filed February 13, 1925, Serial No. 8,956, and in AustriaDecember 19, 1924.

caused by conduction at the fixing points. Therefore the filament havingthroughout equal cross section is hottest in its mid portion.

If such a wire or filament will be used as a source of electrons theoutput owing 16 to the exponential course of the equation of Richardsonis much higher in the intermediate portion than in the end portions ofthe filament. In construct-in a grid electrode for electron discharge tus it is therefore 20 important to well utilize just the interme; diateportion of the filament and thus to approach the grid to the filament inorder to obtain a large rising or pitch of thecharacteristic. But; itwould be wrong to shorten the grid to such an extent that the smallemitting ends of the filament are not covered thereby, since in thiscase, the grid being strongly negative, a definite current flOWiIlgdirectly from the filament to the anode is left, so that the detectingaction will be impaired. It is, of course, not necessary to render thedistance between grid and filament very small at such places, and it isonly sufiicient that the anode be screened off by the grid from the endsof the filament.

From the electrical point of view it is therefore convenient toconstruct the grid so as to form approximately a double cone, i. e. thegrid is strictured in its intermediate portion.

It is a fortunate accident that the said form warrants also goodmechanical properties. It secures a good stiffening and enables a simplefixing of the wires or conductors supporting the grid, since the gridmay be given a larger circumference at the fixing places than washitherto usual. It is even convenient to give the grid at its ends thesame diameter as that of the anode cylinder.

Moreover the probability of a contact taking place between the filamentand the grid is highly reduced by the fact that the small distance beingrequired for enabling a large pitch of the characteristic must only bekept at the intermediate portion of the filament. The double cone gridfaciliates especially the unavoidable subsequent adjusting or settingofthe system of electrodes. Thus if it proves that the filament does notpass exactly centrally through the strictured or narrowed portion ofgrid, this drawback may be obviated by slightly bending the filamentsupportin wireswithout any danger of a contact being caused thereby atthe ends.

The above specified grids may be 'manufactured in many ways, for exampleby winding 9. wire on a core which has approximately the shape of adouble cone and is divided in its width, or by, using suitably punchedsheets.

In the annexed drawings: Figs. 1 and 2 show in an enlarged scale a mostpreferred form of the improved grid in a side and end view respectivelFig. 3 shows by way of example a punc ed metal strip for manufacturingimproved grids. Fig. 4 shows in a perspective view the structure for anelectron dlscharge tube comprising an anode 3, a cathode or filament 4and an improved grid for example made of a length cut from the strip asshown in Fig. 3. Fig. 5 is a perspective view of a tube containing theimproved grid and two other electrodes.

-The grid as shown in Figs. 1 and 2 comprises two end rings. 1, 1 beingconnected ylongitudinal bridges 2, which are bent towards the center orare U-shaped, so as to form the stricture in the mid-portion of thegrid. Fig. 3 shows a preferred form of a punched metal strip which ismanufactured as a continuous band, from which the required lengths maybe cut. Said band comprises two marginal strips 1 connected by bridges 2which are U-shaped. After the strip has been punched the said bridges 2will be bent so as to take a position substantially perpendicular to theplane of the strip. Each len th will be circularly bent and its endswill e secured together 1n any convenient manner. Thus the bridges takean edgewise position and are radially directed toward the filament. Ofcourse a series of other forms and modifications may be designed. Thusthe bridges must not take an edgewise position, also the arrangementneed not be cylindrical and symmetrical, and it is merely essential thatthe grid has in its intermediate portion a smaller distance from thefilament than at its end portions, whereby the said electrical andmechanical advantages will be obtained.

In connection with cylindrical anode and a filament arranged in its axisthe entire surface of grid may take the form of a sur-' face produced inrevolution and being stric- 8 tured or narrowed in its mid-portion.

, What I claim is:

1. In an electron discharge tube a filament and a grid having taperedencl'portions, the distance of said grid from the hottest'pon tion ofthe filament being less than from the tapered end portions thereof, thesaid grid being manufactured of punched sheet metal nected thereby, saidbridges being bent so as and comprising U-shaped longitudinal. bridgesand two supporting end rings conto be directed toward the filament.

2. A strip for manufacturing grids of electron discharge tubes, saidstrip comprising a continuous band from which the required lengths willbe out, said band consisting of two marginal strips which are connectedby U-shaped bridges.

In witness whereof I aifix my signature.

- EDUARD SCHRACK.

